Apparatus for positioning the center of an optical fiber along a predetermined reference axis

ABSTRACT

A positioning apparatus for positioning a point on a cylindrical member having a small diameter, such as an optical fiber, along a predetermined reference axis regardless of the outer diameter of the fiber.

CROSS REFERENCE TO RELATED APPLICATION

This is a continuation of application Ser. No. 07/753,277 filed Aug. 30,1991 (ED-377C), now abandoned, which is itself a continuation-in-part ofapplication Ser. No. 07/631,262, filed Dec. 20, 1990 (ED-377B), nowabandoned, which is itself a continuation of application Ser. No.07/388,546, filed Aug. 2, 1989 (ED-377), now abandoned.

Subject matter disclosed herein is disclosed and claimed in applicationSer. No. 07/838,638, filed herewith, now abandoned, titled "An OpticalFiber Connector Having An Apparatus For Positioning The Center Of AnOptical Fiber Along A Predetermined Reference Axis" (ED-377-E), thatapplication being a continuation-in-part of application Ser. No.07/753,255, now abandoned, (ED-377-D) filed contemporaneously herewiththat application being a continuation-in-part of application Ser. No.07/628,001, filed Dec. 17, 1990, (ED-377-A), now abandoned, which isitself a division of application Ser. No. 07/388,546, filed Aug. 2, 1989(ED-377) (now abandoned).

Subject matter disclosed herein is also disclosed and claimed inapplication Ser. No. 07/753,283, filed contemporaneously herewith, nowabandoned, titled "Opto-Electronic Component Having Positioned OpticalFiber Associated Therewith" (ED-378-A), that application being acontinuation-in-part of application Ser. No. 07/388,548, filed Aug. 2,1989 (ED-378), now abandoned.

BACKGROUND OF THE INVENTION

1. Field Of The Invention

The present invention relates to a positioning apparatus for positioningthe center of an optical fiber or other small dimensioned cylindricalmember, such as capillary tubing, along a predetermined reference axisindependently of variations in the outside diameter of the member.

2. Description Of The Prior Art

Devices are known for positioning an optical fiber so that the axis ofthe fiber is positioned with respect to a reference axis. A typicalexpedient used in such devices is a generally V-shaped groove that isformed in a substrate material and which serves as a cradle to acceptthe fiber being positioned. Representative of such devices is that shownin U.S. Pat. No. 4,756,591 (Fischer et al.), wherein a V-groove isformed in a silicon substrate and an elastomeric member is biasedagainst the fiber to hold it in the groove. The groove may be stepped toprovide a deeper groove segment to hold the jacket of the fiber withinthe device.

U.S. Pat. No. 4,756,591 (Sheem) discloses a grooved silicon substratehaving a pair of intersecting V-grooves therein. A fiber to bepositioned is disposed in one of the grooves while a shim is disposed inthe other of the grooves. The shim may take the form of a tapered or aneccentric fiber, which when respectively slid or rotated under the firstfiber serves to lift the same to bring the axis thereof into alignmentwith a reference axis. A cover may be positioned above the substrate toassist in clamping the first fiber into position.

U.S. Pat. No. 4,802,727 (Stanley) also discloses a positioningarrangement for optical components and waveguides which utilizes aV-grooved structure. U.S. Pat. No. 4,826,272 (Pimpinella et al.) andU.S. Pat. No. 4,830,450 (Connell et al.) discloses arrangements forpositioning an optical fiber that utilize members having frustoconicalapertures therethrough.

It is believed that single crystalline silicon is the material of choiceof the devices above mentioned because of the proclivity of crystallinesilicon to be etched along precise crystallographic planes, thus formingprecise grooves or structural features by photolithographicmicrofabrication techniques. Etchants exist that act upon a selectedcrystallographic plane to a differential degree than upon an adjacentplane, permitting the needed precise control. V-grooves, in particular,can be etched to a controlled width and truncated depth. Under someconditions V-grooves may be etched in a self-limiting operation. Thephotolithographic microfabrication process is generally described byBrodie and Muray, "The Physics of Microfabrication", Plenum Publishing,New York (1982).

Optical fibers include an inner core having a predetermined index ofrefraction surrounded by a cladding layer of a lower index. The innercore is the medium in which the optical energy is guided, while thecladding layer defines the index boundary with the core. The outerdiameter of the fiber may vary in dimension about a predeterminednominal dimension. It has been seen, for example, that two nominallyidentical fibers from the same manufacturer may vary in outsidediametrical dimension by as much as plus or minus four (4) micrometers.This fiber to fiber variation in outer diameter makes difficult theaccurate positioning of the axis of the core of a fiber with respect toa predetermined reference axis using a positioning apparatus having aV-grooved structure.

In view of the foregoing it is believed advantageous to make use of theability of microfabrication techniques to form accurate structures,channels and/or surfaces in a crystalline material to construct apositioning apparatus that will accurately position the center of thefiber, or of any other elongated generally cylindrical member havingsmall dimensions (such as capillary tubing), with respect to apredetermined reference axis. Moreover, it is believed advantageous toprovide a positioning apparatus that consistently aligns thepredetermined point on the fiber or other cylindrical member with thereference axis without requiring great technical skill, expensiveapparatus, and extensive alignment procedures.

SUMMARY OF THE INVENTION

The present invention relates to a positioning apparatus for positioninga predetermined point, such as the geometric center, on the end face ofa cylindrical member, such as an optical fiber, along a predeterminedreference axis. In a preferred case the positioning apparatus includes afirst and a second arm, each of which has at least a first and a secondsidewall that cooperate to define a groove therein. The groove in eacharm is preferably a converging groove so that when the arms are arrangedin superimposed relationship the converging grooves cooperate to definea funnel-like channel over at least a predetermined portion of itslength. The channel has an inlet end and an outlet end and a referenceaxis extending therethrough. A fiber introduced into the inlet end ofthe channel with its axis spaced from the reference axis is displaceableby contact with at least one of the sidewalls on one of the arms toplace a predetermined point on an end face of the member into alignmentwith the reference axis where it is there held by contact with the firstand second arms. To guide the fiber toward the inlet end of the channeleach of the first and the second arms includes a trough therein, eachtrough being disposed on an arm a predetermined distance behind thegroove in that arm, so that in the closed position the troughs cooperateto define a guideway.

The arms having the converging grooves therein may, as is preferred, bemovable from a first, closed, position to a second, centering, position.The superimposed arms are, in this instance, mounted cantileveredfashion, to a foundation. Means is provided for biasing each of the armswith a substantially equal and oppositely directed biasing force towardthe first position. In the preferred implementation the biasing meanscomprises a reduced thickness portion in each of the first and thesecond arms, the reduced thickness portion defining a flexure in eacharm which, when each arm is deflected by contact with the cylindricalmember, generates a force on each arm to bias each arm toward the closedposition.

It should be understood that so long as the arms are movable and biasedtoward the closed position, it is not required that the grooves formedtherein are converging grooves. Accordingly, other positioning apparatusin which the arms are movable but in which the grooves in each of thearms have a form other than a converging groove are to be construed aslying within the contemplation of the invention. Succinctly stated, thepresent invention encompasses any positioning apparatus having arms thatare movable whether the groove in each arm take the form of a converginggroove or a groove of an alternate form. Alternately, the presentinvention also encompasses any positioning apparatus in which the groovein each arm is converging in form, whether the arms are movable or fixedwith respect to each other.

In another aspect, the present invention relates to a fiber-to-fiberconnector formed from confronting pairs of positioning apparatus. Such aconnector is, in the preferred instance, disposed in a housing.

In whatever embodiment realized, it is preferred that the positioningapparatus be fabricated from a crystalline material, such as singlecrystal silicon, using microfabrication techniques. Each structuralelement of the positioning apparatus (viz., each of the arms and eachfoundation) is fabricated in mass on a wafer of silicon. The finishedwafers are aligned, superimposed, and bonded, and each of the resultingpositioning apparatus severed from the finished assembly of bondedwafers. Alignment between superimposed wafers is assured using selectedones of a plurality of alignment grooves on each of the wafers andassociated precise diameter fibers.

In a most preferred embodiment each of the two arms are divided into twoarm segments, or fingers, to compensate for slight misalignments of thegrooves.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be more fully understood from the following detaileddescription thereof, taken in connection with the accompanying drawings,which form a part of this application, and in which:

FIG. 1 is a perspective, exploded view of a positioning apparatus inaccordance with one embodiment of the present invention for positioningthe center point on the end face of an optical fiber with respect to apredetermined reference axis;

FIG. 1A is a definitional drawing illustrating the characteristics of aconverging groove as that term is used in this application;

FIG. 2 is a perspective view of the positioning apparatus of FIG. 1 inthe fully assembled condition;

FIG. 3 is a front elevation view of the assembled positioning apparatusof FIGS. 1 and 2, taken along view lines 3--3 in FIG. 2;

FIG. 4 is a sectional view, in elevation, of the assembled positioningapparatus of FIG. 2, taken along section lines 4--4 in that Figureillustrating the truncated V-groove therein;

FIG. 4A is a view generally similar to FIG. 4 in which a full V-grooveis formed in the positioning apparatus while FIG. 4B is a view generallysimilar to FIG. 4 in which both a full V-groove and a truncated V-grooveare formed;

FIG. 5 is a plan view one of the arms of the positioning apparatus ofFIG. 1 illustrating the relationships of the axes of the groove and theguideway therein;

FIGS. 6A and 6B, 7A and 7B, and 8A and 8B are diagrammatic elevationaland end views of the action of the clips disposed on the arms of thepositioning apparatus shown in FIGS. 1 and 2 in response to theintroduction of a fiber thereinto;

FIGS. 9 and 10 are exploded and assembled perspective views, generallysimilar to FIGS. 1 and 2, of another alternate embodiment of apositioning device in accordance with the present invention in which thearms have nonconverging grooves therein and in which the arms arearticulably movable with respect to each other along one axis only;

FIGS. 11 are 12 are sectional views taken along section lines 11--11 and12--12 in FIG. 10;

FIGS. 13 and 14 are exploded and assembled perspective views, generallysimilar to FIGS. 1 and 2, of another alternate embodiment of apositioning device in accordance with the present invention in whichonly one of the arms has a nonconverging groove therein and in whichboth of the arms are articulably movable with respect to each other;

FIGS. 15 are 16 are sectional views taken along section lines 15--15 and16--16 in FIG. 14;

FIGS. 17 and 18 are exploded and assembled perspective views, generallysimilar to FIGS. 1 and 2, of an alternate embodiment of a positioningdevice in accordance with the present invention in which the arms haveconverging grooves therein and in which the arms are fixed in positionwith respect to each other;

FIG. 19 is an end view taken along view lines 19--19 in FIG. 18;

FIG. 20 is a side sectional view, taken along view lines 20--20 in FIG.18, illustrating the position of the fiber within the channel of the apositioning apparatus in accordance with the alternate embodiment of theinvention shown therein;

FIG. 21 is an exploded isometric view of a pair of positioning apparatusas shown in FIG. 1 used to form a fiber-to-fiber connector in accordancewith the present invention while FIG. 22 is an isometric view of thefully assembled connector of FIG. 21;

FIGS. 23 and 24 are, respectively, a top view in section and a sideelevation section view of a pair of positioning apparatus in accordancethe embodiment of the invention as shown in FIG. 17 used to form afiber-to-fiber connector in accordance with the present invention;

FIGS. 25 and 26 are isometric views of a housing used for thefiber-to-fiber connector shown in FIGS. 21 and 22 in the open and in thepartially closed positions, respectively, while FIG. 27 is a sectionview of the housing of FIG. 25 in the fully closed position taken alongsection lines 27--27 of FIG. 26;

FIG. 28 is a section view generally similar to FIG. 27 of a housing usedfor the fiber-to-fiber connector shown in FIG. 24;

FIG. 29 is a isometric view of an alternate housing for a fiber-to-fiberconnector formed of a pair of positioning apparatus;

FIGS. 30 and 31 are isometric exploded and assembled views,respectively, illustrating the use of a positioning apparatus inaccordance with the present invention to position an optical fiber withrespect to the axis of an edge emitting active device, in which thedevice is surface mounted;

FIG. 31A is a side elevational view generally similar to FIG. 31 showinga positioning apparatus in accordance with the present inventionpositioning a lens with respect to an opto-electronic component;

FIGS. 32 and 33 are isometric exploded and assembled views,respectively, generally similar to FIGS. 30 and 31, illustrating the useof a positioning apparatus in in accordance with the present inventionto position an optical fiber with respect to the axis of a device havingactive surface device, in which the device is mounted to the end of apositioning apparatus;

FIGS. 34A through 34F are end views showing alternate arrangements ofmovable arms each holding a cylindrical member along at least threecontact points in accordance with the present invention;

FIG. 35 is a perspective view of a positioning apparatus having a set offour articulably movable arms in accordance with an alternate embodimentof the present invention for positioning the center point on the endface of an optical fiber with respect to a predetermined reference axis,the mounting foundation being ommitted;

FIGS. 36A and 36B are an isolated perspective views of two of thefingers of the positioning apparatus of FIG. 35;

FIG. 37 is a side elevation view of the assembled positioning apparatusof FIG. 35;

FIGS. 38 and 39 are sectional views of the assembled positioningapparatus of FIG. 37, respectively taken along section lines 38--38 and39--39 in FIG. 37;

FIG. 40 is a top view of the positioning apparatus of FIG. 37 takenalong view lines 40--40 therein;

FIG. 41 is a side elevational view and FIG. 42 is a front elevationalview of the assembled positioning apparatus with the fingers holding afiber in the centering position, the mounting foundation of thepositioning apparatus being ommitted;

FIG. 43 is a front elevational view, similar to FIG. 42 illustrating thesituation extant when the finger pairs are misaligned, while FIG. 44 isa view illustrating the. misaligned finger pairs holding a finger in thecentering position; and

FIG. 45 is a perspective view of an enhanced positioning apparatus thatincludes the positioning apparatus of FIG. 35 and further includes aclamp rearwardly disposed therefrom, the mounting foundation of thepositioning apparatus being ommitted;

FIG. 46 is a perspective view of a wafer used used to fabricate aplurality of arms or foundations used in a positioning apparatus inaccordance with the present invention;

FIG. 47 is a perspective view of a mask used in the photolithographicprocess forming a plurality of arms or foundations for a positioningapparatus in accordance with the present invention;

FIG. 48 is an enlarged view of a portion of the mask used for creating aplurality of arms on the wafer 34;

FIGS. 49A through 49E are schematic representations of the process stepseffected during fabrication of the wafer;

FIG. 50 is is an enlarged view of a portion of the mask used forcreating solder masks on the wafer;

FIG. 51 is an enlarged view of a portion of the mask used for creatingfoundations on the wafer;

FIGS. 52A through 52D are schematic representations of the steps used toform a plurality of fiber-to-fiber connectors from superimposed wafershaving the arms and foundations thereon.

DETAILED DESCRIPTION OF THE INVENTION

Throughout the following detailed description similar reference numeralsrefer to similar elements in all Figures of the drawings.

For purposes of a general overview FIGS. 1 and 2 show a positioningapparatus generally by reference character 20 in accordance with oneembodiment of the present invention in an exploded and in a fullyassembled condition. FIGS. 9 through 12 illustrate a positioningapparatus generally indicated by reference character 20¹ in accordancewith another embodiment, while FIGS. 13 through 16 and FIGS. 17 through20 illustrate still alternate embodiments 20², 20³, respectively, of thepositioning apparatus in accordance with the invention. FIG. 34A through34C illustrate yet another alternate embodiment of a positioningapparatus 20⁴ (having three arms). FIGS. 34D through 45 illustrate yetanother alternate embodiment of a positioning apparatus 20⁵ inaccordance with the invention in which the upper and lower arms havebeen subdivided into upper and lower pairs of arm segments, or fingers.

Although throughout this application the positioning apparatus is castin terms of positioning an optical fiber, it is to be understood thatthe present invention may be effectively utilized with any other memberhaving the form of a small diameter cylindrical object. By way ofexample and not limitation, the positioning apparatus in accordance withthe present invention may be used to position a point disposed, forexample, on the end face of a length of microtubing or capillary tubing.By small diameter it is generally meant less than 0.04 inch (one (1)millimeter), but usually less than 0.020 inch. Moreover, it should befurther understood that the term cylindrical is not to be strictlylimited to an object having a completely circular outer configuration,but would apply to any object whose outer contour is symmetrical to itscentral axis. Thus, again by way of further example and not limitation,the positioning apparatus of the present invention may be used toposition a point disposed, for example, on the end face of a polygonalshaped member or an elliptical member.

As will be developed herein, in the preferred instance each positioningapparatus in accordance with this invention is microfabricated fromsingle crystal silicon or another differentially etchable singlecrystalline material. Crystalline materials are preferred because theypermit the accurate formation of the structural features of thepositioning apparatus in accordance with the present invention using theprocess of differential etching.

Any of the positioning apparatus herein disclosed is useful inaccurately placing or accurately positioning a center point on a fiber,typically a central axial point on the end face of the fiber, intoalignment with a predetermined reference axis and for maintaining thecenter point in alignment with the reference axis. As will be developedthis reference axis itself may be collinearly aligned with respect toanother axis.

By accurately placing or accurately positioning a center point intoalignment with a predetermined reference axis it is meant that a point,such as a point on the end face, of the fiber is brought to within apredetermined distance of the reference axis. This distance is, ingeneral, on the order of a few micrometers (i.e., less than about fivemicrometers) for multi-mode fibers. In the case of a single mode opticalfiber, a positioning apparatus in accordance with the present inventionis especially adapted for positioning a point of the fiber, such as apoint on its end face, to within the precise distance required to coupleeffectively light from the single mode fiber into another fiber or intoan opto-electronic device or to couple effectively light from a source,as a solid state laser, into the fiber. This precise distance is evenless than for multi-mode fibers for comparable coupling loss.

The positioning apparatus in accordance with the invention is alsoadapted for positioning a point on the end face of a multi-mode fiberwith respect to a reference axis.

It should understood that the fiber need not be held by the positioningapparatus at the end face of the fiber in order to obtain the accuratepositioning of the point on the end face into alignment with thereference axis. In practice, the positioning apparatus contacts thefiber a predetermined close distance (on the order of two hundredmicrometers) from the end face. Contacting the fiber at a locationrearwardly from its end face imparts the capability to abut the end faceof a fiber with the end face of a confronting fiber (as in a connector),or to abut the end face of a fiber with a confronting surface of adevice (as in an electro-optical component).

In some instances an enhanced positioning apparatus may be provided inorder to permit more accurate placing or more accurate positioning ofthe point on the end face of the fiber into alignment with respect tothe predetermined axis. To this end, a second positioning apparatus,spaced rearwardly from the first positioning apparatus, may be used tofunction as an alignment clamp for the fiber. This arrangement is seenin FIG. 45. Using an enhanced positioning apparatus, the center point onthe end face of the fiber may be accurately positioned into alignmentwith a predetermined reference axis such that the center point lieswithin a distance of less than one micrometer of the reference axis.

If not apparent from the foregoing, it should also be understood that apositioning apparatus in accordance with the present invention may beused to accurately place or accurately position any other point on thecenter axis of the fiber into alignment with the predetermined axis.

As noted, the cylindrical member preferably takes the form of an opticalfiber. The positioning apparatus of the present invention isparticularly adapted to place a predetermined point P on the end face Eof an optical fiber F along a predetermined reference axis R. Inpractice the point P is the geometric center and lies on the axis A ofthe core C (e.g., FIGS. 6A and 6B and FIGS. 41 and 42) of the fiber F.The core C is itself surrounded by an outer cladding layer L. A jacket Jis provided about the cladding layer L but is stripped from the fiber Fprior to the insertion of the fiber into the positioning apparatus 20.The jacket may comprise more than one layer. As discussed previously,the dimension of the outer diameter D of the cladding layer L of thefiber F may vary from fiber to fiber. Typically this diametricalvariation from fiber to fiber is on the order of three (3) micrometers.This situation makes difficult the positioning of the point P along thereference axis R using the positioning devices of the prior art.

With reference to FIGS. 1 and 2 it is seen that the embodiment of thepositioning apparatus 20 there shown includes a first and a second arm22A, 22B, respectively. Preferably, each of the arms 22A, 22B isidentically formed in a manner to be discussed, so the structuraldetails of only one of the arms, e.g., the arm 22A, will be discussed.It should be apparent, however, that each structural detail of the arm22A finds a counterpart in the other arm 22B. Accordingly, correspondingreference numerals with the appropriate alphabet suffix will denotecorresponding structural details on the arm 22B. If the arms are notsubstantially identical (as, for example, in the embodiments of FIGS. 13through 16 and FIG. 42) adjustments must be made to provide therequisite biasing forces to maintain the point P on the reference axisR.

The arm 22A includes a base portion 24A having a first major surface 26Aand a second, opposed, major surface 28A. The base portion 24A extendsalong the full length of the arm 22A and the dimension of the centralregion 25A of the base portion 24A defines the basic dimension of thearm 22A. A clip generally indicated by the reference character 30A isdefined at a first end of the arm 22A. The clip 30A is formed in arelatively thicker abutment portion 32A that lies on the first surface26A of the arm 22A. The abutment 32A has a planar surface 34A thereonthat preferably lies parallel to the first major surface 26A. To providesome feeling for the physical dimensions involved, the arm 22A has anoverall length dimension on the order of twenty eight hundred (2800)micrometers and a width on the order of three hundred fifty (350)micrometers. In the central region 25A the arm 22A has a thicknessdimension on the order of fifty (50) micrometers, while the remainingportion of the arm 22A has a thickness dimension on the order of onehundred twenty five (125) micrometers.

As may be better seen with reference to FIGS. 3 and 4 a generallyconverging V-shaped groove 36A is defined in the abutment 32A of theclip 30A by generally planar first and second sidewalls 38A, 40A,respectively, and the forward end region of the first surface 26A of thebase 24A. The sidewall 38A has an upper edge 39A (FIG. 1) thereon whilethe sidewall 40A has an upper edge 41A thereon. It should be understoodthat the term "planar" is meant to encompass a surface formed in asingle crystal material by etching in which microscopic steps are ofnecessity produced owing to the lattice structure of the crystal.

With reference now to the definitional drawing of FIG. 1A, the meaningof the term "converging" when applied to a groove in any embodiment ofthe invention herein disclosed (using the reference characters of FIGS.1 and 2) may be made more clear. As used herein, a "converging" grooveis a groove 36 defined from at least two planar sidewalls 38, 40 and hasan enlarged inlet end 42 and a narrower outlet end 43. The respectiveupper edges 39, 41 of the sidewalls 38, 40 of the groove 36 lie in areference plane RP having a reference axis R lying therein. The planarsurfaces 34 also lie in the reference plane RP. The reference axis Rextends in the reference plane RP from the inlet end 42 to the theoutlet end 43 of the groove 36. Each point on the reference axis R isspaced in the reference plane RP an equal perpendicular distance fromthe respective upper edges 39, 41 of the sidewalls 38, 40. The distancebetween the upper edges of the sidewalls and the axis R decreases fromthe inlet end 42 to the outlet end 43 of the groove 36.

The surfaces of the sidewalls 38, 40 are equally and oppositely inclinedwith respect to the reference plane at an angle A greater than zero andless than ninety degrees. The angle of inclination A is determined bythe lattice structure of the crystal, and in the case of (100) silicon,is 54.74 degrees. The projections of the sidewalls 38, 40 intersect in aline L that itself intersects the reference axis R forwardly past theoutlet end 43 of the groove 36. The line L is inclined with respect tothe reference plane RP at an angle B that is greater than zero degreesbut less than ninety degrees. In the reference plane RP the upper edges39, 41 of the sidewalls 38, 40 each converge toward the reference axis Rat an angle C that is on the order of two and one-half to five degrees(2.5 to 5) degrees, and most preferably at about three (3) degrees. Theangle B is dependent upon the values of the angles A and C and typicallythe angle B lies in the range from about four (4) to five (5) degrees.As used herein a "fully funnel-like" channel is a channel that isdefined by the cooperative association of at least two converginggrooves. A "partially funnel-like" channel is a channel that is definedby one converging groove and a surface.

From the foregoing it may be readily understood that a "uniform width"groove is one in which each point on the reference axis R is spaced inthe reference plane RP a uniform distance from the edges 39, 41 of thesidewalls 38, 40 as one progresses from the inlet end 42 to the outletend 43 of the groove 36. The sidewalls of a uniform width groove may beinclined with respect to reference plane RP, or they may extendperpendicularly to it, as desired. A channel formed from one or twouniform width groove(s) is termed a "uniform width" channel. Such achannel may have a rectangular cross section in a plane perpendicularboth to the reference plane and to the reference axis, assuming noinclination of the sidewalls of the groove.

A tapering groove is one in which the planar sidewalls are perpendicularto the reference plane but the distance in the reference plane betweenthe reference axis and the edges of the sidewalls decreases as oneprogresses from the inlet to the outlet of the groove such that theextensions of the planar sidewalls intersect in a line that itselfintersects perpendicularly with the reference axis.

In the embodiment seen in FIGS. 3 and 4 the groove 36 is a converginggroove, and more preferably, is a V-groove truncated by the presence ofa third sidewall defined by a portion of the major surface 26 of the arm22 in which it is disposed. The truncated V-groove has the same depththroughout its length, when measured along a dimension line erectedperpendicular to the surface 34A of the abutment 32A in a directionextending toward the major surface 26A.

It should be understood that the V-shape of the groove 36A may takealternate forms and remain within the contemplation of the invention.For example, as seen in FIG. 4A, the groove 36A may be defined by onlythe first and second sidewalls 38A, 40A, respectively, in which eventthe groove 36A appears as a full V-shape throughout its length. The apex42A of the groove 36A thus appears throughout the full length of thegroove 36A.

FIG. 4B shows another alternative arrangement in which a truncatedV-groove (defined by the first and second sidewalls 38A, 40A,respectively, and the portion of the major surface 26A) extends for somepredetermined axial distance while a full V-groove (defined by the firstand second sidewalls 38A, 40A, respectively) extends for some secondpredetermined distance. Thus, as seen in FIG. 4B, when measured along adimension line erected perpendicular to the surface 34A of the abutment32A in a direction extending toward the major surface 26A the depth thatthe groove 36A extends into the abutment 32A is greater at its inlet end42 (as indicated by the dimension arrow 44A) than it is at its outletend 43 (as indicated by the dimension arrow 46A).

The fully truncated V-groove shown in FIG. 4 is preferred for theembodiment of FIGS. 1 and 2. For purposes of ease of manufacturability,as will be made clear herein, it is also preferred for the embodiment ofFIGS. 1 and 2 that the groove 36A does not converge throughout the fullaxial distance through the abutment 32A. Owing to the provision of tabs48A, 48B (FIGS. 1 and 5) formed near the ends of the abutments 32A, 32B,the sidewalls 38A, 40A defining the groove 36A do not convergethroughout the full length of the groove, but define a short uniformwidth portion just past the converging portion of the groove 36A. Theoverall axial length of the groove 36 (including both the converging andthe uniform width portions) is on the order of three tenths (0.3) of amillimeter, while the uniform width portion of the groove occupies anaxial length of one tenth (0.1) of a millimeter. As is believed bestseen in FIG. 5 the converging and nonconverging portions of the groove36A have a common axis 50A associated therewith.

Again with reference to FIG. 2, an extended enlargement region 54Ahaving a planar surface 56A lies on the base portion 24A of the arm 22Aspaced a predetermined axial distance 58A behind the abutment 32A. Thedistance 58A is on the order of one (1) millimeter. The surface 56A iscoplanar with the surface 34A. The enlargement 54A is provided with anonconverging, uniform width, truncated V-shaped trough 60A defined byinclined planar sidewalls 62A, 64A, respectively, and by a portion ofthe major surface 26A of the base portion 24A near the second endthereof. In the embodiment shown in FIGS. 1 and 2 the trough 60A isuniform in depth along its axial length, as measured with respect to adimension line erected perpendicular to the surface 56A toward the majorsurface 26A. The trough 60A communicates with a converging lead-in 68A.If desired, the walls 62A, 64A may be inclined with respect to eachother so that the trough 60A may be a full V-shape or a partial V-shape,similar to the situation illustrated in connection with FIGS. 4A and 4Bfor the groove 36A. Alternatively, the walls 62A, 64A defining thetroughs 60A, 60B may be parallel or otherwise conveniently oriented withrespect to each other. As is believed best seen in FIG. 5 the trough 60Aand the lead-in 68A have a common axis 70A. The length of the trough 60Aand associated lead-in 68A is on the order of 1.59 millimeter.

FIG. 5 is a plan view of one of the arms 22A. In the preferredimplementation of the embodiment of FIGS. 1 and 2 the axes 50A, 70A(respectively through the groove 36A and the trough/lead-in 60A/68A) areoffset a predetermined distance 72 in the reference plane RP (the planeof FIG. 5). Preferably, the offset 72 is at least one-half thedifference between the diameters of the anticipated largest and smallestfibers to be positioned. As will become clearer herein offsetting theaxes 50A, 70A of the structures 36A, 60A/68A facilitates the centeringaction of the positioning apparatus 20 by insuring that a fiber, as itis introduced into the apparatus 20, is biased to strike one of thesidewalls 38A, 40A forming the groove 36A (and analogously, thesidewalls 38B, 40B forming the groove 36B). This insures wall contactwith the fiber at at least two spaced locations. However, the presenceof the offset 72 necessitates additional manufacturing considerations,as will be discussed. It should be noted that the force resulting frombiasing the fiber in the manner just discussed (or the force on thefiber due to gravity) is much smaller in magnitude than the biasingforce of the arms which serves to center the fiber on the referenceaxis.

In the assembled condition the arms 22A, 22B are disposed insuperimposed relationship one above the other, with the groove 36A, thetrough 60A and the lead-in 68A on the one arm 22A registering with thecorresponding groove 36B, trough 60B and lead-in 68B on the other arm22B. The registered converging grooves 36A, 36B in the abutments 32A,32B cooperate to define a generally fully funnel-shaped channel 92having an input end 94 (FIG. 4) and an output end 96 (FIGS. 4 and 5).(Note that if the tabs 48 are provided, the channel 92 so defined has auniform width portion just preceding the outlet end 96 thereof.) Thereference axis R extends centrally and axially through the channel 92.The reference axis R lies on the intersection of the reference plane RP(which contains the conjoined surfaces 34A, 34B) with the planecontaining the axes 50A, 50B of the converging grooves 36A, 36B.

The registered troughs 60 and lead-ins 68 cooperate to define a guideway98 (FIG. 2). Similarly, the axis R' through the guideway 98 lies on theintersection of the plane containing the conjoined surfaces 56A, 56B ofthe enlargements 54A, 54B (which is the reference plane in the preferredcase) with the plane containing the axes 70A, 70B (FIG. 5) of thetrough/lead-in 60A/68A, 60B/68B. The axes R and R' both lie in thereference plane RP (the plane of the surfaces 34A, 34B, 56A, 56B)although the axes R and R' are laterally offset with respect to eachother in this reference plane by a predetermined offset distance 100(FIG. 1). For a fiber the offset distance 100 is typically on the orderof five (5) micrometers.

The inlet end 94 of the fully funnel-like channel 92 (best seen in FIGS.4 and 5) is sized to circumscribe and thereby to accommodate a fiber Fwhose cladding layer L (or outside surface) has the largest expectedouter diameter dimension. The outlet end 96 of the channel 92 (best seenin FIG. 3) is sized to circumscribe and thereby to accommodate a fiber Fwhose cladding layer L (or outside surface) has a dimension somewhatsmaller than the minimum expected outer diameter dimension of the fiberF. In practice, to position an optical fiber having a nominal outerdiameter dimension of one hundred twenty five (125) micrometers, thelargest expected outer diameter dimension is on the order of one hundredtwenty nine (129) micrometers while the smallest expected outer diameterdimension is on the order of one hundred twenty one (121) micrometers.

The dimension of each of the troughs 60A, 60B is such that the guideway98 so formed by the registered troughs 60A, 60B is sized to accommodatea fiber F whose cladding layer L has the largest expected outer diameterdimension. Despite its dimension with respect to the fiber, the guideway98 assists in the insertion of a fiber into the positioning apparatus 20and is advantageous in this regard.

In the embodiment shown in FIGS. 1 through 5 the surfaces 34A, 34B onthe respective arms 22A, 22B, respectively, are, when in a first,closed, position, either in contact with each other or, if desired,within a predetermined close distance to each other. For optical fibersthe predetermined close distance is typically on the order of five (5)to twenty-five (25) micrometers. In this embodiment the planar surfaces34A, 34B on the abutments 32A, 32B of the clips 30A, 30B are not securedto each other and may move to a second, centering, position, as will bedescribed. The planar surfaces 56A, 56B on the respective arms 22A, 22Bare secured to each other by any convenient means of attachment, as byfusing or soldering. It should be understood that any other mechanicalsecuring expedient may be used to attach or otherwise hold together thesurfaces 56A, 56B to each other.

The positioning apparatus 20 further includes a mounting foundation 74(FIGS. 1 and 2). The mounting foundation 74 is provided with a planarattachment surface 76 thereon. A step 78 in the mounting foundation 74serves to space the attachment surface 76 a predetermined clearancedistance 80 from a second surface 82. The opposite major surface, e.g.,the surface 28A, of the arm 22A is secured, as by fusing or soldering,to the planar attachment surface 76 on the foundation 74. Of course, itshould be again understood that any alternative mechanical attachmentexpedient may be used to attach or otherwise hold together the secondmajor surface of the arm to the foundation 74.

Although the second surface 82 of the foundation is shown in the Figuresas being generally planar in the preferred case, it should be understoodthat this surface 82 may take any desired configuration. As will be morefully appreciated herein, so long as the opposite surface 28A of the arm22A affixed to the foundation 74 is, at least in the region of the clips30A, spaced at least a predetermined clearance distance 80 from thesecond surface 82 (assuming the surface 82 is parallel to the surface76), the movement of the clip on the arm 22A attached to the foundation(in the drawings, the clip 30A) to be described will not be impeded.

When assembled, the clips 30A, 30B disposed at the ends of the arms 22A,22B, respectively, are supported in a cantilevered fashion from theconjoined enlargements 54A, 54B at the opposite ends of the arms. Thearms 22A, 22B are rigid in x-z plane, as defined by the coordinate axesshown in FIG. 1. Moreover, the relatively thin dimension of the centralregion 25A, 25B of the base portion 24A, 24B of the arms 22A, 22Baxially intermediate the respective abutments 32A, 32B and theenlargements 54A, 54B acts as a flexure and permits each arm 22 to flex,springboard fashion, in the directions of the arrows 88 in the y-zplane. As used herein it should thus be appreciated that a flexure is aspring member that is rigid in one plane and is constrained to flex inthe orthogonal plane.

It should further be appreciated that when a clip 30A, 30B is deflectedin its corresponding respective direction 88A, 88B, the resiliency ofthe thinner central region 25A, 25B of the base 24A, 24B, acting as aflexure, defines means for biasing the clips 30A, 30B toward the first,closed, position. The biasing force acts on the clip 30A, 30B in adirection shown by the arrows 90A, 90B, counter to the direction ofmotion 88A, 88B of the arms. The biasing forces must be substantiallyequal and in opposite directions. In general, whatever the number ofarms used in the positioning apparatus, the force on each arm passesthrough the reference axis and the sum of forces when in the centeringposition substantially equals zero. Biasing means employing the thinnercentral region of the base 24 as a flexure (as shown in the FIGS. 1 to4) is preferred for all disclosed embodiments, because when implementedin a single crystal material using a microfabrication technique precisecontrol of the biasing forces is able to be attained. Typically the biasforce on each arm is on the order of five (5) grams.

It should be understood that any other convenient mechanism may be usedto define the means for biasing the arms and the clips 30 thereon towardthe closed position so long as the force on each arm passes through thereference axis and the sum of forces on the arms when they are in thecentering position is substantially equal to zero. Whatever form ofbiasing means is selected the bias force must increase with deflectionof the arm.

Having defined the structure of the positioning apparatus 20 of theembodiment of FIGS. 1 and 2, the operation thereof in positioning apoint P on the center axis and on the end face E of an optical fiber Falong a predetermined reference axis R may be readily understood inconnection with FIGS. 5 through 7.

In operation the fiber F is inserted into the positioning apparatus 20in the direction of the arrow 102 (FIG. 6A). The lead-in portions 68A,68B (FIG. 1) cooperate to guide the fiber F into the guideway 98 (FIG.2) defined by the registered troughs 60A, 60B in the enlargements 54A,54B (FIG. 1). Because the axis R' of the guideway 98 is offset from theaxis R of the fully funnel shaped channel 92 the guideway 98 serves toguide the face E of the fiber F toward the inlet end 94 of the channel92 at a predetermined azimuth with respect to the axis R.

As a result the end face E of the fiber F enters the channel 92 and isinitially displaced, or moved, through contact with at least one of thesidewalls 38A or 38B, 40A or 40B (or portions of the major surface 26A,26B, if these are used to define the grooves 36A, 36B, as in FIG. 4) onone of the clips 30A, 30B, respectively, to the extent necessary to movea predetermined point P on an end face E of the fiber F toward alignmentwith the reference axis R.

At some point on the path of axial insertion of the fiber F into thechannel 92, as the end E of the fiber F moves toward the outlet end 96,the outer diameter of the cladding layer L of the fiber F exceeds thedimension of the channel 92. The arms 22A, 22B respond to a force in thedirections 88A, 88B imposed thereon by the fiber F by moving against thebiasing force from the first, closed, position, shown in FIGS. 7A, 7B,toward a second, centering, position showing in FIGS. 8A, 8B. In thecentering position the clips 30A, 30B open against the bias force actingin the directions 90A, 90B generated by the flexing of the arms 22A,22B, to separate the surfaces 34A, 34B thereon. However, this movementof the arms 22A, 22B from the first toward the second position positionsthe point P on the end face E of the fiber F on the reference axis R.The end face E of the fiber F thus exits through the outlet end 96 ofthe fully funnel shaped channel 92 with the point P precisely alignedwith (i.e., within one micrometer of) the reference axis R, as is shownin FIGS. 8A, 8B. The fiber F is held in this position by contact withthe sidewalls 38A, 38B, 40A, and 40B.

If the tabs 48A, 48B are formed on the abutments 32A, 32B these tabscooperate to define a passage of uniform width along its axial lengththat communicates with the outlet of the funnel-like channel. The fiberF passes through and emerges from such a conduit with the point P on theend face of the fiber still along the reference axis R.

It should be noted that the movement of the arms could be other than theflexing thereof as described heretofore. It therefore lies within thecontemplation of this invention to have the arms move in any othermanner, as, for example, by any form of pinned or jointed (articulated)motion.

With reference now to FIGS. 9 through 12 an alternate embodiment of thepositioning apparatus 20¹ in accordance with the present invention isshown. In this embodiment the arms 22¹ are, similar to the embodimentearlier discussed, articulably movable in cantilevered fashion withrespect to each other against the bias of the flexure defined by thecentral portion 25¹ thereof. However, the grooves 36¹ formed in the arms22¹ are not converging grooves, but are uniform width grooves.Accordingly the channel 92¹ formed by the cooperative association of thearms 22¹ when superimposed one on the other is a uniform width channel.The maximum dimension of such a channel 92¹ in the plane perpendicularto the reference R is less than the outside diameter of the smallestanticipated fiber F.

A further modification to the positioning apparatus 20¹ may be seen fromFIG. 12. It is first noted that the planar walls 62¹, 64¹ of the troughs60¹ are parallel, rather than inclined with respect to each other.Moreover, the offset 100¹ between the axes R and R' lies in the verticalplane, that is, in the plane containing the axes 70¹ of the troughs 60¹,as opposed to being offset laterally (i.e., in the plane containing thesurfaces 56¹). The lead-in portions 68¹ A, 68¹ B are ommitted here butmay be provided.

In operation, a fiber F is inserted into the positioning apparatus 20¹and guided by the passage 98¹ defined by the registered troughs 60¹ A,60¹ B. Because the axis R' of the passage 98¹ is vertically offset fromthe axis R of the channel 92¹ the surface 26¹ B of the arm 22¹ Bbounding the passage 98¹ serves to guide the fiber F toward the inletend 94¹ of the channel 92¹. The fiber F enters the channel 92¹ andcontacts with the edges of the sidewalls 38¹ A, 38¹ B, 40¹ A and 40¹ B.Due to the sizing of the grooves 36¹ A, 36¹ B the fiber F does not touchthe major surface 26¹ A, 26¹ B of the arms 22¹ A, 22¹ B, respectively.The fiber may be chamfered or tapered or a mechanical device may be usedto facilitate insertion of the fiber into the channel 92¹.

Since the fiber F exceeds the dimension of the channel 92¹ the clips 30¹A, 30¹ B are displaced from the first, closed, position toward a second,centering, position. This movement of the clips 30¹ A, 30¹ B maintainsthe point P on the end face E of the fiber F on the reference axis R.The end face E of the fiber F thus exits through the outlet end 96¹ ofthe channel 92¹ with the point P precisely aligned on the reference axisR. The fiber F is held in this position by contact with the edges of thesidewalls 38¹ A, 38¹ B, 40¹ A, and 40¹ B, as indicated by the characterLC.

The embodiment of the positioning apparatus 20¹ shown in FIGS. 9 to 12can be further modified, as seen by the positioning apparatus 20² shownin FIGS. 13 to 16. In this modification, the arm 22² B differs fromthose shown earlier in that no groove is provided therein (FIG. 15). Inthis embodiment, if the groove is a converging groove, a partiallyfunnel-like channel is defined. The fiber F is guided by contact againstthe major surface 26² B and held in position on the reference axis R bycontact with the major surface 26² B and the edges of the sidewalls 38²A, 38² B, again as indicated by the character LC.

FIGS. 17 and 18 are exploded and assembled perspective views, generallysimilar to FIGS. 1 and 2, of another alternate embodiment of apositioning apparatus 20³ in accordance with the present invention whileFIG. 19 shows the end view thereof. In this embodiment, instead of thearms being articulably movable as described earlier, the arms are fixedrelative to each other. Each of the arms 22³ A and 22³ B has aconverging groove therein and the channel 92³ formed by the cooperativeassociation of the arms 22³ when superimposed one on the other is fullyfunnel-like in form. The channel 92³ defines a minimum dimension in theplane perpendicular to the reference R that is, near its outlet end,less than the outside diameter of the smallest anticipated fiber F.

In operation, a fiber F is inserted into the positioning apparatus 20³and guided through the passage 98³ toward the inlet end 94³ of thechannel 92³. The fiber F enters the funnel-like channel 92³ and isguided by contact with one or more of the sidewalls 38³ A, 38³ B, 40³ Aand 40³ B and/or major surfaces 26³ A, 26³ B to place the point P of thefiber F on the axis R. However, since the arms 22³ are fixed withrespect to each other, the fiber F can only advance within the channel92³ to the axial location where the outer diameter of the fiber F equalsthe local dimension of the channel 92³. At this axial location withinthe channel the fiber is held in position by a minimum of four pointcontacts (indicated by the characters PC) between the fiber F and eachof the sidewalls 38³ A, 38³ B, 40³ A, and 40³ B. The dimension of thechannel is such that the fiber is not able to contact the major surfacesof the arms 22³ when it is held along the reference axis R. FIG. 20illustrates the fiber as the same is held within the channel 92³. Theaxial spacing 104 between the end face E of the fiber F and the outletend 96³ of the channel 92³ varies, dependent upon the outer diameterdimension of the fiber F.

The positioning apparatus 20, 20¹, 20² and 20³ in accordance with any ofthe above-described embodiments of the invention may be used in avariety of applications which require the precise positioning of a pointP on the end face E of a fiber F along a reference axis R.

In FIGS. 21 and 22, a pair of positioning apparatus 20-1, 20-2(corresponding to the embodiment shown in FIGS. 1 and 2) are arranged todefine a fiber-to-fiber connector generally indicated by the referencecharacter 120. In this arrangement the apparatus 20-1, 20-2 areconfrontationally disposed with respect to the other so that the outletends 96 of the respective channels 92 therein are spaced a predetermineddistance 122 with the respective reference axes R therethrough beingcollinear. To effect such an arrangement the foundation 74 is extendedin an axial direction and each axial end thereof is provided with aplanar attachment surface 76. Each positioning apparatus 20-1, 20-2 ismounted to its respective attachment surface 76.

The fibers F-1 and F-2 to be connected are inserted into the lead-ins 68of the respective positioning apparatus 20-1, 20-2. Each positioningapparatus 20-1, 20-2, acting in the manner described above, serves toplace the point P on the end face E , of the respective fiber F-1 or F-2along the collinearly disposed axes R. The fibers F-1, F-2 are insertedin to the respective apparatus 20-1, 20-2 until the end faces E on eachfiber abut. The ends E of the fibers F-1, F-2 are secured due to theabove-described holding action of the positioning apparatus. If desiredan suitable index matching adhesive, such as an ultraviolet curingadhesive such that manufactured and sold by Electro-Lite Corporation,Danbury, Conn. as number 82001ELC4480, may be used.

It should be understood that the fiber-to-fiber connector may beimplemented using any of the other of the above-discussed alternativeembodiments 20¹, 20², and 20³ of the positioning apparatus. In the eventa pair positioning apparatus 20³ as shown in FIG. 17 is used (see FIGS.23 and 24), the confronting ends of the positioning apparatus 20³ -1,20³ -2 are preferably abutted and secured, or the pair of positioningapparatus formed integrally with each other. The spacing 122 between theend faces E of the fibers F-1, F-2 is, in this embodiment, defined bythe sum of the distances 104-1, 104-2. The spacing 122 is filled with anindex matching material, such as the adhesive defined above. To thisend, an access port 124 is provided to permit the introduction of theindex matching material into the region between the confronting end faceof the fibers F-1, F-2.

Prior to insertion into the positioning apparatus (of whatever form) itshould be understood that the jacket J (FIG. 29) of the fiber F isstripped in its entirety a predetermined distance from the free endthereof. The exposed portion of the fiber is cleaned with alcohol. Thefiber is cleaved to form the end face E. If desired the end face E maybe ground into a convex shape to yield a point or be lensed.

If desired the fiber-to-fiber connector 120 may be disposed in asuitable housing 130 (FIG. 25). The preferred form of the housing 130 isgenerally similar to that disclosed in U.S. Pat. No. 4,784,456 (Smith),assigned to the assignee of the present invention. This patent is herebyincorporated by reference herein. The housing 130 includes a base 132and a cover 134. The base 132 is, in all cases, provided with a recess136 that is sized to closely receive the connector 120. If the connector120 is realized using any form of the positioning apparatus thatarticulates, the cover 134 must be provided with a corresponding recess138 located so as to permit the articulating motion of the arms ofpositioning apparatus used to form the connector. If the connector 120is realized using the form of the positioning apparatus shown in FIGS.23 and 24, the recess 138 need not be provided. Such a housing 130 isshown in FIG. 28.

The cover 134 is segmented into three sections, 140A, 140B, 140C, eachwhich is hinged to the base 132. The base 132 has, adjacent to each endof the recess 136, V-shaped grooved regions 142A, 142B. The top endsections 140A, 140B each contain respective generally tapered lands143A, 143B. Each of the lands has serrations 145A, 145B respectivelythereon.

In use a connector is inserted in the recess 136 of the housing 130. Itis there held in place by friction but may be otherwise secured ifdesired. The central section 140C of the cover may then be closed, ifdesired. An optical fiber having a predetermined length of its jacket Jstripped and cleaned, is inserted through one of the V-shaped groovedregions 142A, 142B to dispose the stripped end of the fiber into theconnector 120. The grooved region serves to properly orient and positionthe fiber with respect to the connector 120 in the recess 136. Theassociated top end section 140A, 140B, as the case may be, is thenclosed and latched to the corresponding portion of the base 132 (FIG.25, with the fiber ommitted for clarity). When the top is secured to thebase the serrations 145 act against the jacket of the fiber to urge, orto bias, the fiber toward the connector. A second fiber iscorrespondingly introduced into the housing and connector in ananalogous manner. If not already done so, the central section 140C ofthe cover is then closed. The housing 130 is preferably formed byinjection molding.

As seen in FIG. 29, in another form the housing 130 may be implementedusing a mass 160 of index matching material, such as that identifiedabove. The mass 160 extends over both the connector 120 (to embed thesame therein) and some predetermined portion of the jackets J of thefibers F-1, F-2.

The reference axis R on which the point P of the fiber F is positionedmay itself extend collinearly with the axis X of any of a variety ofdevices. Accordingly, a positioning apparatus 20 may be used toaccurately position the point P on the end face E of the fiber F withrespect to the axis X of a particular device 170. FIGS. 30, 31 and FIGS.32, 33 illustrate several examples of the use of a positioning apparatus20 to locate a fiber F along an axis X of a device 170. The device 170may, for example, be realized by any active optical component, such as asolid state laser, a photodiode, a light emitting diode, whether thesedevices are edge active devices or surface active devices. Although inthe discussion that follows the reference character 20 is used toindicate the positioning apparatus, it should be understood that any oneof the embodiments of the positioning apparatus 20¹, 20² or 20³heretofore described may also used.

When used in connection with an edge active device 170 the arrangementin FIGS. 30 and 31 is preferred. In this arrangement the foundation 74is axially extended to define a pedestal 174 at the axial end thereof.The upper surface 176 of the pedestal 174 defines a planar attachmentsurface. The surface 176 is spaced a predetermined distance above theattachment surface 76 or otherwise located such that when the activeoptical component 170 is mounted the surface 176 the axis X of thedevice 170 and the reference axis R are collinear. With the axes R and Xcollinear, the positioning of the point P on the fiber F along the axisR will automatically position that point P in the same relationship withthe axis X. The device 170 must be accurately mounted on the surface 176so that its axis X is collinearly aligned with the axis R.

To mount the device 170 the surface 176 may be provided with a layer ofsolder layer, such as a gold/tin solder. The device 170 may have acorresponding layer of the same material. The device 170 is positionedon the surface 176 using a suitable micropositioning apparatus, such asa vacuum probe. The device is aligned to the edge, heated above themelting point of the solder and cooled, so that the solder forms a bond.

When used with a surface active device, as seen in FIGS. 32 and 33, theactive surface of the device 170 is secured to the front surface 178 ofthe pedestal 174. Attaching the device to the front surface 178 isbelieved to provide sufficient bonding area to secure the device 170 tothe positioning apparatus 20. The surface 176 of the pedestal 174 isrelieved to avoid obstruction between the active region of the device170 and the end face E of the fiber F.

It should also be appreciated, as is illustrated in FIG. 31A, that thepositioning apparatus in accordance with any one of the embodimentsheretofore described may be configured to accurately position a lens,such as a ball or a rod lens L, with respect to the axis X of the device170 (whether the same is an edge active or a surface active device). Thepositioning apparatus would be modified to provide a seat 31S in theclips thereof sized to accept the lens L.

In addition to the various embodiments of the two-armed configurationsfor the positioning apparatus 20, 20¹, 20² and 20³ of the presentinvention previously disclosed, it lies within the contemplation of thisinvention for a positioning apparatus in accordance with this inventionto exhibit more than two arms 22.

In this regard FIGS. 34A to 34C generally illustrate a positioningapparatus 20⁴ having three arms 22A, 22B and 22C.

FIGS. 34D through 34F generally illustrate a positioning apparatus 20⁵having four arms 22A, 22B, 22C and 22D. A detailed description of anembodiment of a four armed positioning apparatus 20⁵ is set forthhereinafter.

The extension to even greater number of arms would be readily apparentto those skilled in the art.

Generally speaking, in FIG. 34A each the arms are configured similar tothe form of the arms discussed above. The arms may, if desired carry agroove, although it should be understood that such is not required. InFIGS. 34B and 34E the arms are configured from rods. Although the rodsshown as round in cross section it should be understood that they canhave any desired alternate cross section. In FIGS. 34C and 34F the armsare configured in a generally planar bar form. As will be fully setforth herein, in FIG. 34D the four arms may be formed by sawing theupper and lower arms (indicated by the characters 22A, 22B in FIGS. 1 to4) along a cut line extending perpendicular to the major surfaces 26 and28 of each of the arms, thereby to define upper and lower pairs of armsegments, or "fingers". As used in this application, the term "fingers"is to be understood to be the structures defined when an "arm", as thatterm has been used herein, is subdivided into two axially elongatedsegments.

However configured the arms are shown in FIGS. 34A through 34F asangularly juxtaposed in a surrounding relationship to the channel 92defined their cooperative association. Similar to the situationdescribed heretofore the resiliency of the arms defines the biasingmeans which urge the arms toward the closed position. However, it shouldbe understood that the biasing means may be otherwise defined, so longas the force on each arm passes through the reference axis and the sumof forces on the arms when they are in the centering position issubstantially equal to zero. Whatever form of biasing means is selectedthe bias force must increase with deflection of the arm. The arms actagainst the fiber F inserted into the channel along the various lines ofcontact LC illustrated in FIG. 34 to maintain the predetermined point onthe fiber on the reference axis R.

In practice, during fabrication of the positioning device misalignmentmay sometimes occur between the first and second arm in the arm pair(FIG. 1). As a result, in use, the fiber may be supported by only twodiametrically opposed sidewalls on the first and second arms (see FIG.43). Thus, the fiber may not be positioned to lie along the referenceaxis.

A positioning apparatus 20⁵ in accordance with the embodiment of theinvention shown in FIGS. 35 through 40 is believed able to avoid thisresult. With reference to these Figures it is seen that each arm (22⁵ A,22⁵ B, FIG. 35) is itself longitudinally slit along slit lines 21⁵thereby to define a set of four fingers, 22⁵ -1, 22⁵ -2, 22⁵ -3, 22⁵ -4,arranged into a first, upper, pair of fingers (22⁵ -1, 22⁵ -2) andsecond, lower, pair of finger pairs (22⁵ -3, 22⁵ -4).

As shown in FIG. 36A, in a manner generally similar to the earlierdiscussed embodiments, each finger in the set includes a base portion24⁵ having a first major surface 26⁵ and a second, opposed, majorsurface 28⁵. The base portion 24⁵ extends along the full length of eachfinger and the dimension of the central region 25⁵ of the base portion24⁵ defines the basic dimension of each finger.

A clip generally indicated by the reference character 30⁵ is defined ata first end of each finger 22⁵. The clip 30⁵ is formed in a relativelythicker abutment portion 32⁵ that lies on the first surface 26⁵ of eachfinger 22⁵. The abutment 32⁵ has a planar surface 34⁵ thereon thatpreferably lies parallel to the first major surface 26⁵. Again, toprovide some feeling for the physical dimensions involved, the finger22⁵ has an overall length dimension on the order of twenty four hundred(2400) micrometers and a width on the order of eight hundred (800)micrometers. In the central region 25⁵ each finger 22⁵ has a thicknessdimension on the order of one hundred (100) micrometers.

Each abutment 32⁵ includes a planar sidewall 33⁵ that extends in aninclined manner (at an angle of 54.74°) from the perpendicular to themajor surface 26⁵ of each finger. The sidewalls 33⁵ in the fingers ofthe first pair 22⁵ -1 and 22⁵ -2 cooperate to define a uniform widthgroove 36⁵ while the sidewalls 33⁵ in the fingers in the other, mating,finger pair 22⁵ -3 and 22⁵ -4 also cooperate to define a similar uniformwidth groove 36⁵.

Each finger has, at the end opposite the abutment 32⁵, an enlargementgenerally indicated by the reference character 54⁵. The enlargement hasabutments 55⁵ A and 55⁵ B thereon. Each abutment 55⁵ A is provided witha wall 62⁵ that cooperates with the corresponding wall 62⁵ on the otherfinger in the pair and with a portion of the major surface 26⁵ of thebase portion 24⁵ near the second end thereof to form a nonconverging,uniform width, truncated V-shaped trough 60⁵. In the embodiment shown inFIGS. 35 and 36 the trough 60⁵ is uniform in depth along its axiallength, as measured with respect to a dimension line erectedperpendicular to the surface 56⁵ A extending toward the major surface26⁵. The trough has an axis 70⁵ extending centrally and axiallytherethrough. The trough 60⁵ is wider than the width dimension of thegroove 36⁵. In a more preferred arrangement the trough 60⁵ communicateswith a converging lead-in 68⁵ defined by the cooperative association ofsurfaces 69⁵ provided on each abutment 55⁵ A on the fingers in the pair.

A most preferred arrangement has two angled surfaces at each lead-incorner of each abutment, as shown in FIG. 36B. Abutments 32⁵ lookedsimilar to the abutments 55⁵ A before a cut is made to form the linearfront edges of the abutments 32⁵, as shown in FIG. 36B. As will becomeclearer herein, the surfaces 56⁵ A on the abutments 55⁵ A of opposedfinger pairs are joined, by any convenient means of attachment, as byfusing or soldering. In FIG. 36B the lateral surfaces of the abutments32⁵ and the abutments 55⁵ A are ramped or inclined with respect to themajor surfaces 26⁵.

The surface 56⁵ B on the the abutment 55⁵ B depending from the surface28⁵ is spaced a predetermined distance 80⁵ from the surface 28⁵ of thefinger 22⁵. As will also become clearer herein, the abutment 55⁵ Bthereby functions as a standoff to space the finger away from afoundation or slab on which it is mounted.

In the assembled condition, best shown in FIGS. 35 and FIGS. 37 through40, corresponding fingers in each pair are disposed in superimposedrelationship one above the other, with the groove 36⁵ and the trough 60⁵cooperatively defined by the fingers in one pair registering with thecorresponding groove and trough formed by the cooperative action of thefingers in the other pair.

The grooves 36⁵ formed by the cooperative action of the fingers in eachpair are themselves registered and thus cooperate to define a channel92⁵ (FIGS. 35 and 39). The channel 92⁵ has an input end 94⁵ and anoutput end 96⁵. The reference axis R extends centrally and axiallythrough the channel 92⁵. Preferably, the reference axis R lies in areference plane RP₁ containing the surfaces 56⁵ A on each finger 22⁵(see FIG. 38). Most preferably, the reference axis R also lies in asecond reference plane RP₂ (FIG. 39)containing the slit lines definingeach pair of fingers in the finger set. It should be understood thatmanufacturing tolerances can result in slight misalignment of axis Rwith respect to the reference plane RP₂. The consequences of such amisalignment will be discussed more fully hereafter.

The registered troughs 60⁵ (and lead-ins 68⁵, if present) cooperate todefine a guideway 98⁵ (FIGS. 36B and 38). The axis R' through theguideway 98⁵ lies in the plane containing the conjoined surfaces 56⁵ Aof the abutments 55⁵ A (see FIG. 38). The plane RP₂ (FIG. 38) containsthe axes of the troughs. The axes R and R' both lie in the referenceplane RP₁ (the plane of the surfaces 56⁵ A) and should preferably bothlie in the reference plane RP₂.

In the embodiment shown in FIGS. 35 through 40 the surfaces 34⁵ onopposed corresponding fingers in each pair are, when in a first, closed,position, either in contact with each other or may, as preferred, bewithin a predetermined close distance to each other to insure they willnot be affected in joining operations. For optical fibers thepredetermined close distance is typically on the order of one (1) to two(2) micrometers. The planar surfaces 34 are not secured to each otherand thus may move to a second, centering, position, as will bedescribed.

As seen in FIG. 35 the positioning apparatus 20⁵ further includes, inthe preferred instance, a mounting slab 74⁵ having a planar attachmentsurface 76⁵ thereon. The surface 56⁵ B of the abutment 55⁵ B on eachfinger 22⁵ -3, 22⁵ -4 is secured, as by fusing or soldering, to theplanar attachment surface 76⁵ on the slab 74⁵. Owing to the presence ofthe abutment 55⁵ B, the surfaces 28⁵ on the fingers 22⁵ -3, 22⁵ -4 ofthe lower pair are spaced the distance 80⁵ from the attachment surface76⁵. It should be understood that the abutment 55⁵ B may be omitted, andthe lower fingers 22⁵ -3, 22⁵ -4 may be mounted to a foundation 74having a step 82 thereon similar to that shown in FIG. 1, in order toprovide the clearance distance 80⁵ necessary to permit the movement ofthe lower fingers in each pair. The fingers 22⁵ -1, 22⁵ -2 in the upperpair of fingers may also be secured, as by fusing or soldering, to theplanar attachment surface 76⁵ on a second slab 74⁵. The second slab 74⁵is shown in outline in FIG. 35.

When assembled, as shown in FIG. 35, the clips 30⁵ disposed at the endsof the fingers 22⁵ are supported in a cantilevered fashion from theconjoined enlargements 54⁵ at the opposite ends of the fingers. Each ofthe fingers 22⁵ is relatively rigid in x-z plane, as defined by thecoordinate axes shown in FIG. 35. Moreover, the relatively thindimension of the central region 25⁵ of the base portion 24⁵ of eachfinger 22⁵ axially intermediate the respective abutments 32⁵ and theenlargements 54⁵ acts as a flexure and permits the clips 30⁵ at the endof each finger 22⁵ to flex, springboard fashion, in the directions ofthe arrows 88⁵ in the y-z plane. Again, as the term is used herein, aflexure is a spring member that is relatively rigid in one plane and isconstrained to flex in the orthogonal plane.

It should further be appreciated that when a clip 30⁵ is deflected inits corresponding respective direction 88⁵ the resiliency of the thinnercentral region 25⁵ of the base 24⁵, acting as a flexure, defines meansfor biasing the fingers 22⁵ and the clips 30⁵ thereon toward the first,closed, position. The biasing force acts on each clip 30⁵ in a directionshown by the arrows 90⁵ counter to the biasing directions 88⁵. It shouldbe understood that any other convenient mechanism may be used to providethe means for biasing the clips 30⁵ toward the closed position. Thebiasing forces must be substantially equal and in opposite directions.Biasing means employing the thinner central region 25⁵ of the base 24⁵as a flexure is, however, again preferred because when implemented in asingle crystal material using a microfabrication technique precisecontrol of the biasing forces is able to be attained. Typically the biasforce on each finger is on the order of twenty (20) grams.

Having defined the structure of the positioning apparatus 20⁵ inaccordance with this embodiment of the invention, the operation thereofin positioning a point P on the center axis and on the end face E of anoptical fiber F along a predetermined reference axis R may be readilyunderstood in connection with FIGS. 38 through 43. As mentioned earlier,and as is clearly visible in FIG. 41, when positioning the point P intoalignment with the reference axis R the positioning apparatus actuallycontacts the fiber at contact points lying a close distance from the endface E.

Assuming that the reference axis R (FIG. 39) of the channel 92 alignswith both the first and second reference planes RP₁, RP₂ (FIG. 38), theoperation of the positioning device 20⁵ is substantially identical withthe operation of the positioning device shown and discussed earlier inconnection with FIG. 6 through 8. Thus, the fiber F is inserted into thepositioning apparatus 20⁵ in the direction of the arrow 102⁵ (FIGS. 37,41). The fiber F is inserted into the guideway 98⁵ defined by theregistered troughs 60⁵. The fiber F enters the channel 92⁵ and isinitially displaced, or moved, through contact with at least one of thesidewalls 33⁵ or portions of the major surface 26⁵ used to define thegrooves 36⁵ on one of the clips 30⁵ to the extent necessary toaccurately place a predetermined point P on an end face E of the fiber Ftoward alignment with the reference axis R.

Since the outer diameter of the cladding layer L, shown on FIGS. 41 and42, of the fiber F exceeds the dimension of the channel 76⁵ formed bythe sidewalls the fingers 22⁵ respond to a deflecting force in thedirections 88⁵ imposed thereon by the fiber F by displacing from thefirst, closed, position (shown in FIG. 39) toward a second, centering,position shown in FIGS. 42 and 43. In the centering position the clips30⁵ open against the bias force acting in the directions 90⁵ generatedby the flexing of the fingers 22⁵ to separate the surfaces 34⁵ thereon.This movement of the finger 22⁵ from the first toward the secondposition accurately positions the point P on the end face E of the fiberF in alignment with the reference axis R. The end face E of the fiber Fthus exits through the outlet end 96⁵ of the channel 92⁵ with the pointP accurately positioned in alignment with the reference axis R, as isshown in FIGS. 34 and 42. The fiber F is held in this position bycontact with the sidewalls 33⁵.

As alluded to earlier, in some instances, owing either to misalignmentbetween arms (before they are slit to form finger pairs), misalignmentbetween the slit lines 21⁵ in each finger pair and the desired locationof the slit lines on each arm, mismatches of finger thickness, and/ormismatches of finger widths, the assembled position of the superimposedfinger pairs will appear as shown in FIG. 43. Diametrically oppositesidewalls 33⁵ on diametrically opposite abutments 32⁵ are not equallyspaced from the reference axis R. The misalignment of the arms (prior toslitting to form finger pairs) is indicated by the reference characterM_(a). The misalignment of resulting slit lines 21⁵ is indicated by thereference character M_(s-1) and M_(s-2). The mismatches of fingerthickness is indicated by the reference character M_(t). The mismatchesof finger width is indicated by the reference character M_(w).

As seen in FIG. 43 when a fiber F is inserted into the channel 92⁵formed from arms or fingers with such misalignment(s), the fiber F willfirst strike a first, and then the second, of two diametrically opposedramping lateral surfaces of the lead-ins of the abutments 32⁵ (FIG. 36B)before contacting the sidewalls 33⁵. These initial contact points on thefingers 22⁵ -2, 22⁵ -3 are illustrated in FIG. 44 at referencecharacters 33⁵ I. Those sidewalls 33⁵ first contacted by the fiber F areforced apart in the directions 93⁵ A, 93⁵ B. However, since the biasforces generated by the movement of the first contacted sidewalls areopposite, the fiber F becomes centered in an interim centered positionin a plane parallel to and centrally between such two surfaces. Thisinterim centered position lies at some point in the plane indicated inFIG. 44 by the line denoted at reference character P₁.

Continued advancement of the fiber F through the channel 92⁵ causes theouter diameter of the fiber F to touch one or both of the remainingsidewall pair. The first touch of the fiber to the sidewalls 33⁵ is notthe final position of the fiber. The final position of the fiber isachieved when the two fingers on the sidewall pair 22⁵ -1, 22⁵ -4 (FIG.44) have moved sufficiently to center the fiber. These final contactpoints are illustrated in FIG. 44 at reference characters 33⁵ F. Sincethe bias forces created by movement of these last two sidewalls are alsoequal and oppositely directed the fiber is finally centered on theintersection of the plane P₁ and another plane P_(F). The plane P_(F)plane is parallel to and centrally located between the two surfacestouched at the contact points 33⁵ F.

The final position of the fiber F may be displaced from the desiredreference axis due to the misalignments defined earlier and to othervariations within manufacturing tolerances as described below. To make apositioning apparatus, or a connector or an opto-electronic componentutilizing the same, for typical single mode optical fibers, thepositioning apparatus must be able to handle fibers ranging in diameterfrom 125 to 128 micrometers. This range is found to be the typicaldiameter variation in quality single mode fibers.

To insure that a fiber is held properly by all four fingers in the mostpreferred embodiment (FIGS. 35 to 45) the alignment of wafers forbonding during the fabrication process to be discussed must limitvariation of the misalignment in the direction across the grooves (thedimension M_(a) of FIG. 43) to + or -9.5 micrometers. This direction ofmisalignment reduces the range of fiber diameter variation that arehandled in the most preferred embodiment. The misalignment of wafers inthe other direction, along the length of the reference axis should be nomore than twenty (20) micrometers. This direction of misalignmentresults in the clamping points of one pair of side-by-side fingers beingaxially displaced from those points of the other pair of side-by-sidefingers, which would tend to bend the fiber slightly upwardly ordownwardly.

The misalignment of the slit or saw cut, (M_(s) in FIG. 43) must be nomore than ten (10) micrometers to avoid cutting into a sidewall of agroove when the slit width is sixty-six (66) micrometers wide, asobtained by using a typical sixty (60) micrometer saw.

The thickness of the flexure portion of the fingers should not vary bymore than + or - three (3) micrometers so spring forces will be balancedwith the fiber centered.

Commonly held tolerances in the microfabrication arts, such as in themicrofabrication of devices as pressure rupture discs, are well withinthe above ranges. In fact, assuming the use of an enhanced positioningapparatus having an alignment clamp, as shown in FIG. 45, estimatesshow, in practice, the above maximum variations would result in

±5 micrometers for sidewise misalignment, M_(a),

±1.5 micrometers for for flexure thickness M_(t),

±10 micrometers for axial misalignments of wafers.

Other variations such as flexure width and friction encountered when afiber is centered by actions of the four fingers are small. The netresult using commonly achievable manufacturing tolerances formicrofabricated parts is well under one (1) micrometer in displacementof the center point on the end face of the fiber from alignment with thereference axis. Even for the maximum variations discussed above, thedisplacement of the center of the fiber end face from alignment with thedesired reference axis is well under one (1) micrometer.

With reference to FIGS. 42 and 44 (whether the fingers are mismatched ornot) since the fiber is supported only at points of contact between eachof the fingers in each finger pair, the length of the fiber behind thecontacts is free to pivot. To avoid this eventuality it is desirable toenhance the ability of the positioning apparatus to precise position afiber into alignment with a reference axis. To this end, it lies withinthe contemplation of the present invention to provide a clamp, generallyindicated by the reference character 220, for engaging the fiber apredetermined distance 224 along the reference axis from the vicinity ofthe points of contact between the fiber F and the fingers 22⁵. Such anenhanced positioning apparatus 20⁵ E is shown in FIG. 45.

As is best seen in FIG. 45, the enhanced positioning apparatus 20⁵ Ecomprises a first, forward, positioning apparatus 20⁵ and a clamp 220disposed a predetermined distance 224 behind the positioning device 20⁵.The clamp 220 is preferably implemented using a second positioningapparatus 20⁵. However, any other of the positioning apparatus 20, 20¹,202, 20³ or 20⁴ disclosed herein may be used as the clamp 220. Moreover,the clamping function may be performed by any arrangement of suitableform.

It is, of course, understood that an enhanced positioning apparatussimilar to that shown by reference character 20⁵ E in FIG. 45 may beobtained using a forward and rearward "arrangement of positioningapparatuses. Any combination of positioning apparatus 20, 20', 20", 20³,20⁴, or 20⁵ as disclosed herein may be used to implement the forwardpositioning apparatus and the clamp, thereby to form an enhancedpositioning apparatus 20⁵ E.

The clamp 220 serves to position accurately a point on the center axisof the fiber into alignment with the reference axis. This second pointon the center axis of the fiber is spaced a predetermined distance fromthe end face of the fiber. By providing the clamp 220, any angularmisalignment between the fiber axis and the reference axis is held to aminimum.

It should also be apparent, similar to the situation disclosed in FIGS.30 through 33, that a positioning device 20⁵ or an enhanced positioningapparatus 20⁵ E in accordance with this invention can be used with anedge active or a surface active opto-electronic device to define anopto-electronic component.

In such a usage, the slab 74⁵ would be extended, in the manner shown inFIGS. 30 and 31, to provide a pedestal similar to the pedestal 174, onwhich an edge active device 170 may be mounted. The device 170 may bemounted to the pedestal in the manner earlier discussed. Alternatively,the slab may be modified to provide a pedestal similar to that shown inFIGS. 32 and 33, to accept a surface active device 170. As is the casein the earlier, the device 170 may take the form of a solid state laser,a photodiode, or a light emitting diode, whether these devices are edgeor surface active. The axis X of the device is collinear with thereference axis of the positioning apparatus 20⁵ so that a fiber alignedby the apparatus 20⁵ with the reference axis will be in alignment withthe device 170. The positioning apparatus 20⁵ may be modified assuggested in FIG. 31A, if desired, to accept a lens.

If it is desired further, it should be appreciated that the positioningapparatus 20⁵ or an enhanced positioning apparatus 20⁵ E in accordancewith this invention can be used to fashion a connector apparatus forholding the facial ends of two confronting fibers each in alignmentalong a predetermined common reference axis.

To this end it is advantageous to mount onto the slab 74⁵ a twoconfrontationally disposed positioning apparatuses 20⁵ or twoconfrontationally disposed enhanced positioning apparatuses 20⁵ E, (or acombination of the same).

The connector arrangement of positioning apparatuses 20⁵ or apparatuses20⁵ E may be disposed in a suitably adapted housing generally similar tothat shown in FIGS. 25 to 28, it being understood that the referencecharacter 120 in FIGS. 25 to 29 indicates a connector formed ofconfronting apparatus 20⁵ or apparatuses 20⁵ E. Most preferably, thehousing should be fabricated material with a low thermal coefficient ofexpansion over a temperature range from (-45° F. to +85° F.). A suitablepreferred material is a liquid crystal polymer such as that sold byHoechst Celanese Corporation under the mark "Vectra". Conventionalmolding processes for that polymer can be used to form the housing.

The photolithographic microfabrication technique used to manufacture apositioning apparatus in accordance with this invention may beunderstood from the following discussion taken in connection with FIGS.46 to 52. Although the discussion is cast in terms of the manufacture ofa fiber-to-fiber connector using the preferred embodiment of theenhanced positioning apparatus 20⁵ E as shown in FIG. 45, the teachingsare readily extendable to the manufacture of any of the embodiments ofthe positioning apparatus heretofore described, including their use inthe various other applications previously set forth. (For clarity ofdescriptive text, the basic reference characters (i.e., withoutsuperscripts) of the elements of the positioning apparatus are used.)

A silicon wafer 200 having an appropriate predetermined crystallographicorientation is the starting point for fabrication of the arms 22 of apositioning apparatus 20 in accordance with the present invention. Itshould be understood that other single crystalline substrate materials,such as germanium, may be used provided appropriate alternative etchantsand materials compatible with the selected alternative substrate areused. The wafer 200 is polished on at least one surface. Suitablesilicon wafers are available from SEH America, Inc., a subsidiary ofShin-Etsu Handotai Co. Ltd., Tokyo, Japan, located at Sparta, N.J. Itshould be understood that the wafer 200 can be of the "p-type", "n-type"or intrinsic silicon.

The substrate material is preferably (100) surface silicon because thismaterial can be etched by anisotropic etchants which readily act uponthe (100) crystallographic plane but substantially do not etch the (111)plane. As a result the preferred truncated V-shaped grooves 36A, 36B,the troughs 60A, 60B, the lead-ins 68A, 68B and the central region 25A,25B of the arms 22A, 22B between the abutments 32A, 32B and theenlargements 54A, 54B are easily formed. The width and depth of suchfeatures are dependent upon the preselected width of the opening in thephotolithographic mask being used and the time during which the etchantsare permitted to act. Etchants operate on 100 surface silicon in anessentially self-limiting manner which property is useful in forming afull V-groove. One of skill in the art will recognize that if othercross-section configurations are required, other predeterminedcrystallographic orientations of the silicon may be used. For example,if square cross-section features are desired, (110) surfaces siliconwafers can be used. Other cross sectional configurations for thefeatures are, however, significantly more expensive and, as will be seenlater, would require a more complicated configuration to obtain thefiber centering action equivalent to that inherent in a V-groove.

FIG. 46 is a plan view of the wafer 200. The wafer 200 has peripheralflats 201 and 202, as specified by the SEMI Standard. The flats 201, 202primarily indicate orientation of the crystallographic structure of thesilicon and are also used for wafer identification and mask alignment.The longer flat 201 indicates the direction of crystallographic plane(110). The shorter flat 202 is placed a predetermined angular amount onthe periphery of the wafer with respect to the flat 201, the magnitudeof the angle depending upon the doping of the crystal.

As will be developed, the peripheral regions 203 of the wafer 200, whenprepared, carry alignment features, while the central region 204 of thewafer 200 has the structural features of the arm or foundation, as thecase may be, of the positioning apparatus formed thereon.

FIG. 47 shows a mask 210 with a patterns 212 of alignment features, suchas orthogonal alignment grooves or alignment through holes 212H andcorresponding wells 212W, thereon. The holes 212H are etched from theopposite surface of the wafer as are the wells.

If grooves are used, the grooves in each pattern 212 are graduated insize to accommodate various sized (diameter) quartz alignment fibers.The grooves 212 have a V-shaped cross section to accept fibers rangingin width from about 0.004825 inches (0.123 mm) to 0.005000 inches (0.127mm) in 0.039370 inch (0.1 mm) steps, five grooves 212 having beenillustrated. The groove width (at the open top of the groove) is largerthan the diameter of the fiber so that the center of the fiber issubstantially coplanar with the surface of the wafer when the fiber isdisposed in its associated groove. Accordingly, for a 0.123 mm fiber, agroove 0.1506 mm is provided. Similarly, for a 0.124 mm fiber, the opentop dimension of the groove is 0.1518 mm. For a 0.125 mm fiber, the opentop dimension of the groove is 0.1531 mm; for a 0.126 mm fiber the opentop dimension of the groove is 0.1543 mm.; and for a 0.127 mm fiber, theopen top dimension of the groove is 0.1555 mm.

A central area 214 of the mask 210 has provided thereon a repetitivepattern 220 (one of which is shown in FIG. 48) containing to apredetermined number of structural features (i.e., arms or foundationsmor slabs) of the positioning apparatus 20 being formed. Since thetypical wafer 200 is about 3.9381 inches (101.028 mm) in diameter and atypical connector 120 measures about three hundred fifty (350)micrometers at the widest location and is about two thousand eighthundred (2800) micrometers in length, the structural features forapproximately one thousand (1000) connectors 120 may be formed from thecentral region 204 of the wafer 200.

FIG. 48 is an enlarged view of a portion 220 of the pattern provided onthe central region 214 of the mask 210. In FIG. 48, the patternillustrated is that used to form a plurality of conjoined arms 22 usedin a connector 120. The pattern 220 is formed on the surface of thecentral region 214 of the mask 210 using a well-known step and repeatprocess to cover the entire area.

The repetitive pattern 220 shown in FIG. 48 is comprised of a pluralityof columns 224 which are defined between an array of adjacent parallelscribe lines 226 and a first and a second separation line 227A and 227B.Each column 224 contains ten (10) discrete zones 228A through 228E thatare symmetrical within the column 224 about a cutting line 230.

Seen between two next adjacent scribe lines 226 is the configuration oftwo arms 22 joined front end to front end. Seen between three nextadjacent scribe lines 226 is the configuration of two arms 22 joinedlengthwise side to side. The zone 228A corresponds to features definingthe region of the lead-in 68A of an arm 22A. The zone 228B correspondsto features defining the region of the trough 60A of the arm 22A.Similarly, zone 228C corresponds to the central portion 25A of the arm22A, while the zone 228D corresponds to features defining the region ofthe converging groove 36A on the arm 22A. The axis 50A of the converginggroove 36A is offset from the axis 70A of the trough 60A by the offsetdistance 100. Finally, if provided, the zone 228E corresponds tofeatures defining the region of the tabs 48A of an arm 2² A. Note thatin the mask illustrated in FIG. 36 the position of the offset 100 on oneside of the cutting line 230 is reversed from the position of the offset100 on the opposite side of the cutting line, although this arrangementis not necessarily required.

The repetitive pattern for a mask of the arm 22B will be similar to thatshown in FIG. 48 except that the direction of the offset distances 100for the arm 22B will be the mirror image of the pattern for the arm 22A.As will become clearer herein, this mirror image relationship betweenthe offsets is necessary so that so that features on the resulting arms22A, 22B will register with each other when one is inverted andsuperimposed on the other. Of course if the offset 100 is eliminated,masks for the arms 22A and 22B will be identical.

The cross-hatched areas shown in FIG. 48 preferably correspond to thoseareas of the central region of the wafer 200 that will be protected by alayer of resist material (as will be described) while the areas shownwithout hatching will be left unprotected during subsequent etchingsteps. A negative resist is employed but it should be apparent that thelocation of the hatched and clear areas of FIG. 48 may be reversed ifdesired. This would alter somewhat subsequent steps, but in a mannerknown to those in the art.

FIGS. 49A through 49E illustrate the process steps whereby a wafer 200of crystalline silicon may be formed into an array of arms 22Acorresponding to the array shown on the mask of FIGS. 47 and 48. As seenin FIG. 49A the wafer 200 is preliminarily covered with a layer 232 of amaterial that acts in a manner similar to a mask. Silicon dioxide (SiO₂)is preferred, and is surfaced onto the polished operative surface 200Sof the silicon wafer 200 by thermally growing the silicon oxide layer inan oxygen atmosphere at elevated temperature (circa eleven hundred fifty(1150) degrees Celsius), as is known. As indicated, silicon oxide isused because available etchants that attack silicon will also attackknown photoresists but will attack the oxide only slightly. This slightattack is accounted for when dimensioning the photomask.

The layer of silicon oxide 232 is then covered with a photoresist 234.Preferred is a positive resist, such as the mixture of 2-ethoxyethylacetate, N-butyl acetate and xylene sold by Shipley Company,Incorporated of Newton, Mass., as "Microposit Photoresist" 1400-37. Theresist is spun onto the surface of the silica dioxide in accordance withinstructions set forth in the Shipley Microelectronic Products Brochure(1984) using standard apparatus such as that available from HeadwayResearch Incorporated of Garland, Tex. under model number ECR485.

The mask 210 is mounted atop the wafer 200 and is aligned with respectto the flats 201, 202 of the wafer 200 using alignment bars 235. Thus,in a finished wafer the alignment grooves 212 are precisely positionedwith respect to the flats on the wafer through the use of alignment bars213 on the mask. The wafer 200 is exposed to ultraviolet light throughthe mask 210 and subsequently developed.

Since a positive resist is used the unexposed areas of the resist arewashed away using de-ionized water, leaving the layered arrangement ofexposed, hardened resist 234, silicon dioxide 232 and wafer 200, asshown in FIG. 49B.

Next the pattern of the mask 210 is etched into the silica layer 232.Buffer hydrofluoric acid (HF) is preferred. This step results in thearrangement shown in FIG. 37C. Those skilled in the art will recognizethat process variables such as, for example, concentration, time andtemperature are all adjusted appropriately to optimize results in all ofthe wet processing steps described.

Thereafter, a second, differential, etching step is performed to etchthe silicon to form the features of the arms 22A. The preferredanisotropic etchant is ten percent (10%) potassium hydroxide (KOH).Ethylene diamine ("ED") pyrocatechol ("P") and water, in a mix of 750 mlED, 120 gm P and 240 ml water, may be used. This etching produces thestructural feature in the surface of the silicon illustratedschematically in FIG. 49D by reference character 236. The depth of thefeature 236 is controlled by controlling the etching time, as is wellknown. Of course, differential etching is self-limiting for the insideangles of the structure, if left to proceed.

The silicon dioxide layer 232 is then removed by etching with bufferhydrofluoric acid (HF) and another layer of silica, i.e., silicondioxide, is grown on the surface. Next, resist is deposited on thesurface of the wafer and is imaged through a mask, as shown FIG. 38.This results in a layer 238 of hardened resist being formed on thosepredetermined portions of the wafer that are to be bonded (correspondingto zones 228C through 228E and to troughs 60 (see FIG. 36)).

The silica layer is then etched from areas that are to be bonded (See,FIG. 49E) using hydrofluoric acid (HF). The resist layer 238 is strippedusing acetone, leaving a finished wafer ready for bonding.

This completes the fabrication of the first wafer 200 having the arrayof arms 22A thereon.

As noted earlier, since the axis of the guideway 98A may be offset fromthe axis of the groove 92A, the mask for the arms 22B may not beidentical with the mask used to form the arms 22A. Accordingly, a secondwafer having an array of arms 22B thereon may be prepared in accordancewith the method steps illustrated in FIG. 49. The finished second wafer(not specifically illustrated but hereinafter referred to by character200') is similar in all respects except in location of the offset 100. fthe wafers are the same, the second wafer is prepared exactly as thefirst.

A third wafer 200" is prepared using a foundation mask, a portion ofwhich is shown in FIG. 51. FIG. 51 is an enlarged view of a portion ofthe pattern 220' provided on the central region of the foundation mask(analagous to the pattern of the arm mask shown in FIG. 36). Therepetitive pattern 220' is comprised of a plurality of columns 244 whichare defined between an array of adjacent parallel scribe lines 246 and afirst and a second separation line 248A and 248B. Each column 244contains four (4) discrete zones 250 that are symmetrical within thecolumn 244 about a center line 252. The zones 250A define mountingsurface 76 on a foundation 74. The zones 250B correspond to the surfaces82 provided on the foundation. The wafer 200" containing the foundations74 is exposed in a manner analogous to that shown in FIG. 37, with theexception that the exception that the solder mask exposure is notcarried out. However, the layer of silica is removed from the surface ofthe wafer 200".

Having prepared wafers for the arms 2² A (the wafer 200), the arms 22B(the wafer 200') and the foundations 74 (the wafer 200"), the finalassembly of the connector 120 may be made as is shown in FIG. 40.

The wafer 200' is placed on top of the wafer 20. Preferred methods ofaligning wafers to be joined involve etching holes that go through onewafer and wells (shallow holes) on the mating wafer accurately locatedby the precision photomasks used for etching so that wafers are alignedby matching through hole with well at at least two locations on eachwafer. One method involves etching truncated pyramidal through-holes andwells so that when one wafer is turned over and placed against thesecond wafer, each hole and well can be matched by observation with amicroscope as the wafers are positioned with precision adjustmentmechanisms as are well known in the micromachining art. A better methodis to etch V-grooves forming crosses as holes and wells and matching byinfrared source and camera searching for the brightest image made by abeam passing through both wafers. Such infrared equipment iscommercially available, (as, for example, from Research Devices Divisionof American Optical Corporation) a most preferred method is to etch agrid pattern of lines spacing from each other on the order of ten (10)micrometers separation. An infrared beam image can be inspected for thebrightest and most uniform lines in the image where etched lines arealigned letting the most infrared beam through the two silicon wafers.(This latter method is believed to be accurate to 0.5 micrometer, ascompared to the method with crosses which is accurate to, typically, ten(10) micrometers.

As yet another alternative, the registration of the features on thewafer 200' to those on the wafer 200 is effected using at least two andpreferably four lengths of a stripped optical fiber and thecorresponding appropriate one of the alignment grooves in each array 212of grooves. The diameter of each length of the optical fiber is measuredby micrometer, accurate to plus or minus 0.5 micrometers. Each of thefibers is placed in groove in the groove array 212 that most closelycorresponds to the measured diameter. Each alignment fiber thus sits inthe selected alignment groove such that the axis of the alignment fiberlies in the plane of the surface of the wafer 200 with the remainingportion of each fiber protrudes above that surface.

The wafer 200' is inverted and placed atop the wafer 200, with thecorresponding grooves in the wafer 200' receiving the protrudingportions of the alignment fibers thereby to precisely align the patternof the two wafers. Since the alignment grooves on each wafer are formedsimultaneously with the formation of the features on the wafer, andsince the mask for each wafer is formed optically one from the other,precise alignment between the wafers is achieved. It is noted in FIGS.40A and 40B only one of the fibers 254 and grooves 121 is shown, forclarity of illustration.

In a less preferred method, the assembly of superimposed wafers 200,200' shown in FIG. 52 is bonded in a wet controlled atmosphere furnaceaccording to methods described in the paper by Shimbo et al.,"Silicon-to-silicon direct bonding method" published 10/86 in theJournal of Applied Physics, and in the paper by Lasky et al., "Siliconon Insulator (SOI) By Bonding and Etchback", IEDM 85. As seen in FIG.52B the exterior surface 256' of the wafer 200' is lapped to reduce itsthickness from it original thickness (typically approximately seventeen(17) mils) to a final thickness of five (5) mils.

The more preferred method of bonding uses the above but avoids expensivelapping by etching parts of the arms and fingers as described below andavoids forming an abutment on the slab.

The resulting bonded structure is inverted and the exterior surface 256'of the wafer 200' is mounted atop the wafer 200". The alignment of thesewafers is effected using a fixture employing quartz blocks 260 abuttingagainst the flats 201, 202 of the wafer 200. The wafer 200' is thenbonded to the wafer 200". It is to be understood that other bondingtechniques, such as those discussed in the paper by Wallis and Pomerantz"Field Assisted Glass-Metal Sealing" published 9/69 in the Journal ofApplied Physics may be used to bond the wafers. Still other alternatebonding techniques would include metallic or glass solder bonding.

The exterior surface 256 of the wafer 200 is then lapped until thedimension of the wafer 200 is that of the wafer 200'. Thus, thesubstantial equality of the biasing forces imposed by the flexure isprovided.

The resultant three wafer bonded stack shown in FIG. 52D may then becut. Only the top two wafers 200, 200' of the bonded stack (containingthe arms 22-1B, 22-2B and the arms 22-1A, 22-2A, respectively, FIG. 22)are first cut along the lines in the wafers corresponding to the cuttinglines 230, 230' on the arm masks (FIG. 36). This cut is made using ablade that is on the order of 0.003 inches to create the distance 122 inFIG. 22. The bonded stack is thereafter cut, using a blade that is 0.015inches thick, along the lines in the wafers corresponding to theseparation lines 227A, 227B on the wafer 200, the separation lines227A', 227B' on the wafer 200', and the separation lines 248A, 248B onthe wafer 200", as well along the scribe lines 226, 226' and 246 (on therespective wafers 200, 200' and 200") all of which are registered witheach other, thereby to yield from the bonded stack about one thousand ofthe fiber-to-fiber connectors 120.

As noted earlier, the positioning apparatus 20⁵ shown in FIGS. 35through 44 or an enhanced positioning apparatus 20⁵ E shown in FIG. 45(and any connector or opto-electronic made using the same) is fabricatedin a manner generally similar to that previously discussed in the caseof the positioning apparatus 20. Some specific points may be noted.

A portion of the top surface of a wafer defines the surface 56⁵ B of afinger pair when fabrication is completed. An adjoining portion of thewafer is etched to form the surface 28⁵ of each finger pair.

On the opposite side of the wafer, a portion of that surface becomessurface 56⁵ A of each abutment 54⁵, while another portion of that wafersurface is etched to form surface 34⁵ of the abutment 32⁵ of each clip30⁵. An adjoining portion of that surface of the wafer between thesurfaces 56⁵ A and 34⁵ is etched slightly to form the major portion ofthe surface 26⁵ defining the flexure. The abutments 54⁵, 32⁵ are alsoetched to form sidewall surfaces 62⁵, 33⁵ respectively. Each sidewallsurface 62⁵, 33⁵ defines an angle of 54.74 degrees from the plane of thewafer due to the silicon crystal structure.

It is noted that the etching process used does not make sharp corners atthe ends of a groove. What would have been a corner is etched inward oneach side thereof. Due to the crystal structure of the silicon twoangled faces are formed at a corner location as shown in FIG. 36B. Theright angle corners shown in the Figure are formed by sawing or cutting.The beveled corners formed are advantageous since they serve as guidesto bring a cylindrical object, as the fiber, into the channels 90⁵ and92⁵ formed by the troughs 60⁵ and the grooves 36⁵, respectively.

Several finger pairs are etched in a single silicon wafer. All etchingis done before the other fabrication steps.

A wafer containing containing a predetermined number of unseparated offingers is positioned on top of another wafer containing a correspondingpredetermined number of unseparated of fingers. The wafers are alignedso that the surfaces 56⁵ A (see FIGS. 36A) of the unseparated fingers oneach wafer surface are touching in contact. The slight etching of eachwafer relieves the surfaces 34⁵ on each unseparated finger to preventtheir touching and being joined.

The two wafers containing the unseparated fingers are placed on a thirdwafer which contains a number of unseparated slabs 74⁵.

The wafers are joined, only at surfaces 56⁵ A, by heating, to fusiontemperature in an oven. Known methods of joinder such as soldering canalso be used.

After the joining steps are completed the silicon wafers are sliced orcut, (i) down the centers of the grooves 90⁵,92⁵ (through the abutments30⁵ and optionally, but preferably through the abutments 54⁵) toseparate cooperating sets of fingers, (ii) to separate sets of fourfingers which will become positioning apparatus, and (iii), to cut thebottom wafer. The bottom wafer may be separated to define a mountingslab for a set of four fingers to serve as a positioning apparatus (asin FIG. 35), to contain a both a forward and a rearward set of fourfingers to define as a positioning apparatus with a rearward clamp (asin FIG. 45), or to contain two confrontationaly disposed positioningapparatus, (each of which may include a single positioning apparatus, ora positioning apparatus having the forward and rearward finger set.

Those skilled in the art, having the benefits of the teachings of thepresent invention as hereinabove set forth, may impart numerousmodifications thereto. It should be understood that such modificationsas herein presented and any others are to be construed as lying withinthe contemplation of the present invention, as defined by the appendedclaims.

What is claimed is:
 1. A positioning apparatus for positioning acylindrical member comprising:a first and a second arm, at least thefirst arm having at least a first and a second sidewall cooperating todefine a groove therein, the arms being arranged in superimposedrelationship, each arm being movable from a first, closed, position to asecond, centering, position, means for biasing each of the arms with asubstantially equal and oppositely directed biasing force toward thefirst, closed position, in the closed position the arms cooperating todefine a channel having a reference axis therethrough, the channelhaving an inlet end and an outlet end, each of the arms being arrangedsuch that a cylindrical member introduced into the inlet end of thechannel with the axis of the member spaced from the reference axis isinitially displaceable by contact with at least one of the arms to movea center point on an end face of the member toward alignment with thereference axis, the arms being responsive to further axial movement ofthe member through the channel by moving against the bias force towardthe centering position to position the point on the end face of themember into alignment with the reference axis by contact between themember and both the first and the second arms.
 2. The positioningapparatus of claim 1 wherein the first and the second sidewalls in thefirst arm cooperate to define a converging groove therein, the channelbeing partially funnel-like in shape over at least a predeterminedportion of its axial length.
 3. The positioning apparatus of claim 2wherein the second arm has a planar surface thereon.
 4. The positioningapparatus of claim 1 wherein the second arm has at least a first and asecond sidewall disposed therein, the first and second sidewalls in thesecond arm cooperating to define a converging groove therein, theconverging groove in the first arm and the converging groove in thesecond arm cooperating to define the channel, the channel being fullyfunnel-like in shape over at least a predetermined portion of its axiallength.
 5. The positioning apparatus of claim 4 further comprising afoundation, the first arm being mounted to the foundation.
 6. Thepositioning apparatus of claim 5 wherein the foundation and the firstand the second arms are each fabricated from a crystalline material. 7.The positioning apparatus of claim 4 wherein biasing means comprises areduced thickness portion in each of the first and the second arms, thereduced thickness portion defining a flexure in each arm which, wheneach arm is deflected by contact with the member, generates a force oneach arm to bias each arm toward the closed position.
 8. The positioningapparatus of claim 7 wherein the first and the second arms are eachfabricated from a crystalline material.
 9. The positioning apparatus ofclaim 4 wherein each of the arms has a major surface thereon, a portionof the major surface connecting the first and the second sidewalls andcooperating to define the groove therein, wherein the converging grooveso defined in each arm has a truncated V-shape.
 10. The positioningapparatus of claim 4 wherein each arm has a trough disposed therein,each trough being disposed on an arm a predetermined distance behind thegroove in that arm, in the closed position the troughs in the armscooperating to define a guideway for guiding the member toward thechannel.
 11. The positioning apparatus of claim 10 wherein the guidewayhas an axis therein, the axis of the guideway being offset from the axisof the channel by a predetermined distance.
 12. The positioningapparatus of claim 1 wherein the first and second sidewalls in the firstarm cooperate to define a groove having a uniform width dimensionthroughout its length, the channel being rectangular in cross sectionalshape over at least a predetermined portion of its axial length.
 13. Thepositioning apparatus of claim 12 wherein the second arm has at least afirst and a second sidewall disposed therein, the first and the secondsidewalls in the second arm cooperating to define therein a groovehaving a uniform width dimension throughout its length, the uniformgroove in the first arm and the uniform groove in the second armcooperating to define the channel, the channel being rectangular incross sectional shape over at least a predetermined portion of its axiallength.
 14. The positioning apparatus of claim 13 wherein each sidewallof the groove in the first arm and each sidewall of the groove in thesecond arm has an edge thereon, the edges of the sidewalls contactingthe member.
 15. The positioning apparatus of claim 12 wherein the secondarm has a planar surface thereon and wherein each sidewall of the groovein the first arm has an edge thereon, the edges of the sidewallscontacting the member.
 16. The positioning apparatus of claim 1 whereineach arm has a trough disposed therein, the troughs in the armscooperating to define a guideway for guiding the member therebetween.17. The positioning apparatus of claim 16 wherein the guideway has anaxis therein, the axis of the guideway being offset from the axis of thechannel by a predetermined distance.
 18. The positioning apparatus ofclaim 1 wherein biasing means comprises a reduced thickness portion ineach of the first and the second arms, the reduced thickness portiondefining a flexure in each arm which, when each arm is deflected bycontact with the member, generates a force on each arm to bias each armtoward the closed position.
 19. The positioning apparatus of claim 1further comprising a foundation, the first arm being mounted to thefoundation.
 20. The positioning apparatus of claim 19 wherein thefoundation and the first and the second arms are each fabricated from acrystalline material.
 21. The positioning apparatus of claim 1 whereinthe first and the second arms are each fabricated from a crystallinematerial.
 22. The positioning apparatus of claim 1 wherein each of thearms has a major surface thereon, a portion of the major surfaceconnecting the first and the second sidewalls and cooperating to definethe groove therein, wherein the groove so defined in each arm has atruncated V-shape.
 23. A positioning apparatus for positioning acylindrical member having an outer diameter falling within apredetermined range of diameters, the positioning apparatus comprising:aset of four fingers, each of the fingers having a sidewall thereon, eachfinger being articulably movable from a first, closed, position to asecond, centering, position, in the closed position the sidewalls of thefingers cooperating to define a channel having a reference axistherethrough, the channel having an inlet end and an outlet end, meansfor biasing each of the fingers toward the first, closed position with apredetermined biasing force such that the sum of the biasing forces onthe fingers when the fingers are in the centering position issubstantially equal zero, each of the fingers being arranged such that acylindrical member introduced into the inlet end of the channel with theaxis of the member spaced from the reference axis is initiallydisplaceable by contact with the sidewall on at least one of the fingersto move accurately a center point on an end face of the member towardalignment with the reference axis, each of the fingers being responsiveto further axial movement of the member through the channel bydeflecting against its biasing force to position the center point on theend face of the member into alignment with the reference axis by contactbetween the member and a point of contact on each of the fingers. 24.The positioning apparatus of claim 23 wherein each of the fingers isaxially elongated and has a first and a second axial end thereon, andwherein the sidewall is disposed at the first axial end, each fingerhaving a reduced thickness region disposed thereon intermediate thefirst and the second axial ends, the reduced thickness portion defininga flexure in each finger which, when each finger is deflected by contactwith the member, generates a restoring force on each finger to bias eacharm toward the closed position
 25. The positioning apparatus of claim 24wherein the fingers are arranged into a first and a second pair offingers, each pair of fingers being mounted to a slab.
 26. Thepositioning apparatus of claims 23 wherein each of the fingers isfabricated from a crystalline material.
 27. The positioning apparatus ofclaim 23 wherein the fingers are arranged into a first and a second pairof fingers, at least one pair of fingers being mounted to a slab. 28.The positioning apparatus of claim 23 further comprising:an alignmentclamp for engaging the member at a predetermined distance along thereference axis from the vicinity of all of the contact points on thesidewalls of the fingers, the clamp engaging the member so as toposition accurately a predetermined second point on the center axis ofthe member into alignment with the reference axis.
 29. The positioningapparatus of claim 28 wherein the alignment clamp comprises:a secondpositioning apparatus itself comprising:a second set of four fingers,each of the fingers in the second set having a sidewall thereon, eachfingers in the second set being articulably movable from a first,closed, position to a second, centering, position, in the closedposition the sidewalls of the fingers in the second set cooperating todefine a second channel having a second reference axis therethrough, thesecond channel having an inlet end and an outlet end, the secondreference axis being collinear with the first reference axis, means forbiasing each of the fingers in the second set toward the first, closedposition with a predetermined biasing force such that sum of the biasingforces on the fingers in the second set when the same are in thecentering position is substantially equal zero, each of the fingers inthe second set being arranged such that a cylindrical member introducedinto the inlet end of the second channel with the axis of the memberspaced from the second reference axis is initially displaceable bycontact with the sidewall on at least one of the fingers in the secondset to move the center point on the end face of the member towardalignment with the second reference axis, each of the fingers in thesecond set being responsive to further axial movement of the memberthrough the channel by deflecting against its biasing force to move thesecond point on the center axis of the member toward alignment with thesecond reference axis, each of the fingers in the second set alsodeflecting against its biasing force to position accurately thepredetermined second point of the member into alignment with thereference axis by contact between the member and a point of contact oneach of the fingers in the second set.
 30. The positioning arrangementof claim 29 wherein each of the fingers in the second set is axiallyelongated and has a first and a second axial end thereon, and whereinthe sidewall is disposed at the first axial end, each finger in thesecond set having a reduced thickness region disposed thereonintermediate the first and the second axial ends, the reduced thicknessportion defining a flexure in each finger in the second set which, wheneach finger in the second set is deflected by contact with the member,generates a restoring force on each finger in the second set to biaseach such finger toward the closed position.
 31. The positioningarrangement of claim 30 wherein the second positioning apparatus ismounted to the slab.
 32. The positioning arrangement of claim 29 whereineach of the fingers in the second set is fabricated from a crystallinematerial.
 33. The positioning arrangement of claim 29 wherein thefingers in the second set are arranged into a first and a second pair offingers.